Catalyst compositions comprising manganese oxide promoted by titanium, tin or lead on alumina



United States Patent CATALYST COMPOSITIONS COMPRlSlNG MAN- GANESE OXIDEPROMOTED BY TlTANlUM, TEN 0R LEAD ON ALUMINA Ruth E. Stephens, Detroit,Daniel A. Hirschler, Jr., Birmingham, and Frances W. Lamb, Detroit,Mich, assignors to Ethyl Corporation, New York, N.Y., a corporation ofVirginia No Drawing. Filed May 1, 1962, Ser. No. 191,638

3 Claims. (Cl. 252-463) This application is continuation-in-part of ourapplication Serial No. 23,915 filed April 22, 1960, now abandoned.

This invention relates to manganese catalysts. More particularly, theinvention relates to catalysts comprising manganese oxide and optionallya promoter metal supported on a specific transitional alumina. Theinvention also relates to a method of substantially oxidizing thehydrocarbon and carbon monoxide constituents which are present in theexhaust gas of internal combustion engines.

In recent years extensive research has been devoted to the alleviationof air pollution in many metropolitan areas. Part of this effort hasbeen directed to methods of reducing the unburned hydrocarbons andcarbon monoxide emitted with the exhaust gas of internal combustionengines. Various catalytic converter systems have been proposed toaccomplish this purpose. With such systems the exhaust gases are passedthrough a catalytic bed Wherein the noxious materials are converted toan inactive form.

In our earlier filed application Serial No. 23,915 We have described andclaimed catalysts which are especially eifective for the oxidation ofhydrocarbon and carbon monoxide constituents of exhaust gases. Thesecatalysts consist of transitional activated alumina having a surfacearea of at least 75 square meters per gram and a silica content of notmore than 5 percent on which is impregnated or with which is mixed,manganese oxide such that the catalyst system contains between 0.5 and25 percent of manganese in an oxide form. It was also found that undercertain conditions, the inclusion of a small amount of another metal ormetals further enhanced the properties of those catalysts. As describedtherein, those catalysts promote the oxidation of a great percentage ofhydrocarbon and carbon monoxide emitted with the exhaust gas stream.Moreover, those catalysts are extremely resistant to the many catalystpoisons contained in the exhaust gas stream of current internalcombustion engines.

Among the catalysts disclosed in the aforementioned application, acertain group has outstanding catalytic properties. The purpose of thepresent application is to specifically claim this highly preferredembodiment. The catalysts of the present invention comprise manganeseoxide and optionally a promoter metal supported on a specific type oftransitional alumina. When this particular type of transitional aluminais used, superior manganese catalysts are obtained, even more efficientthan manganese catalysts wherein other seemingly similar transitionalaluminas are used.

It is an object of this invention to provide novel oxidation catalysts.Another object is to provide oxidation catalysts which are active andwhich retain their high degree of efficient during long periods of use.Another object is to provide a method to substantially oxidize theunburned hydrocarbons and carbon monoxide found in the exhaust gasstream of internal combustion engines.

The objects of this invention are accomplished by providing novelcatalysts especially adapted to substantially oxidize the unburnedhydrocarbon and carbon monoxide constituents of the exhaust gas ofinternal combustion engines, said catalyst comprising a transitionalalumina carrier impregnated with or mixed with from about 0.5 to 25percent maganese in an oxide form and optionally from about 0.5 to 10percent of a promoter metal, said transitional alumina comprising amixture of from about 10 to 85 percent of chi, 10 to 85 percent of alphamonohydrate and from 5 to about 45 percent amorphous forms oftransitional alumina, said transitional alumina further characterized bycontaining from 0.02 to about 5 percent silica and having a surface areaof at least square meters per gram. The transitional alumina carriers ofthis invention are substantially free of the eta form of transitionalalumina. The present invention also embodies the method of substantiallyoxidizing unburned hydrocarbons and carbon monoxide contained in theexhaust stream of internal combustion engines which comprises passingsaid exhaust gas over and through the above-described catalysts.

By the use of the catalysts of this invention, substantial amounts ofthe carbon monoxide are converted to carbon dioxide and a largepercentage of the unburned hydrocarbons are completely oxidized tocarbon dioxide and water. Further, the catalysts of this invention areactive over a wide temperature and under a wide variety of operatingconditions. Other important aspects of the catalysts of this inventionare excellent thermal stability at extremely high temperatures and thatthey do not catlyze the oxidation of nitrogen. Still another advantageis the resistance of these catalysts to the many potential catalystpoisons found in exhaust gas such as the products of combustion oforganolead anti-knock agents and other additives found in currentcommercial gasolines. In spite of such an extremely adverse environment,the present catalysts operate efiiciently over long periods of time.

The catalysts contemplated by this invention contain from about 0.5 to25 percent manganese in an oxide form and from 0.5 to about 10 percentof a promoter metal. In many applications an optimum concentration isfrom about 4 to 15 percent manganese and from about 2 to 5 percent of apromoter metal. With a freshly prepared catalyst, the manganese ispresent in one of its oxidized states. The promoter metal may be presentin the metallie state or as an oxide. When in actual operation, thecatalyst system is very complex, but the metals no doubt fluctuatethrough various oxidation states depending upon temperature and thenature of the environment.

As disclosed in the aforementioned application Serial No. 23,915, avariety of transitional aluminas are useable to obtain excellentmanganese catalysts. therein, transitional aluminas are meta-stableforms which, in general, are produced by heating of alpha or betaalumina trihydrate or of alpha alumina Inonohydrate. As each of thesestarting materials or any mixture thereof is heated, phase changes takeplace. A number of intermediate or transitional alumina phases areformed. These are characterized by being only partially or poorlycrystalline. They are partly amorphous and partly crystalline. Formationof these phases is reversible; on rehydration they can be converted backto the starting ma terials. On prolonged heating, particularly at veryhigh temperatures such as 1150 C., they are converted into the so-calledalpha alumina which is a stable, refractory type of alumina.

As described In the overall transition between the alumina hydrates andalpha alumina, several different transitional aluminas are prepared,either simultaneously or concurrently. Some of these transitional phasesare convertible to others upon proper heating or cooling. According tothe nomenclature used in the pamphlet Alumina Properties, Russell et al,published by the Aluminum Company of America, Pittsburgh, Pennsylvania,1956; the names assigned to the various transitional aluminas are gamma,delta, eta, theta, kappa, chi and rho. In addition, the alphamonohydrate itself is in a sense a transitional alumina since it is aproduct reversibly obtained on heating of either alpha or beta aluminatrihydrate under suitable conditions of temperature and time. Inaddition to the forms described above, there is an amorphous aluminawhich is characterized by having no definitive X-ray diffractionpattern. However, some workers have assigned a characteristic broadX-ray line at 4.5 A. to amorphous alumina. Amorphous alumina is theleast crystalline of the principle alumina phases. In a sense thisalumina can also be considered to be transitional, for upon heating, itsstructure may be converted to other forms of transitional alumina.

It appears not possible to describe each transitional alumina in termsof its specific physical properties other than those mentioned above.Many can be characterized by their X-ray diffraction pattern. Several ofthese are reproduced on page 28 of the pamphlet referred to above.

While many of the above-described transitional aluminas may be used toobtain excellent oxidation catalysts, we have found that the use of oneparticular combination of transitional aluminas results in superiormanganese catalysts. Such catalysts are more efiicient and have a longerlongevity than otherwise similar manganese catalysts but using anotherform of transitional alumina. In other Words, a particular type oftransitional alumina is specific for manganese catalysts and ispreferred over other forms of apparently closely related transitionalaluminas.

The transitional aluminas used in the catalysts of this inventioncomprise a mixture of the chi, alpha monohydrate and amorphous forms oftransitional aluminas. It is essential that the transitional aluminamixture contain from 10 to 85 percent alpha monohydrate, 10 to 85percent chi and from 5 to 45 percent amorphous forms of transitionalaluminas. The aluminas useful as carriers of this invention aresubstantially free of the eta form of transitional alumina. A preferredtransitional alumina carrier of this invention comprises a mixture ofabout 40 percent chi, about 40 percent alpha monohydrate and about 20percent amorphous forms of transitional alumina.

In addition to the inherent transitional nature of the alumina itself,certain other properties are essential for use as carriers of thisinvention. The most important of these is the surface area/mass ratioand the content of silica, SiO The transitional alumina must have asurface area/mass ratio of at least '75 square meters per gram and asilica content of from about 0.02 to 5 percent. In order to functionefficiently according to this invention, the transitional alumina mustmeet both these requisites. If the surface area is greater than theabove minimum but the silica content does not fit within theabovedescribed limits, the alumina does not function well. By the sametoken, if silica content is between 0.02 and 5 percent but the surfacearea is below 75 square meters per gram, the alumina does not functionas a carrier of this invention. Nor does it so function if neither thesilica content nor the surface area is Within the above specifications.

In illustration of the importance of the above properties, we havetested aluminas with surface areas as high as 350 m. gr but with silicacontent greater than 5 percent. These have resulted in catalysts withinferior prop erties with respect to exhaust gas conversion. Also, thealumina with a silica content less than 5 percent but with a surfacearea of only 0.5 m. g. was ineffective as a support for manganese oxide.

It is not possible to ascribe definite preparative procedures toprepartion of the transitional aluminas of this invention. Conversion ofthe starting material-alpha and beta alumina trihydrates and alphaalumina monohydratesto one or more of the various transitional aluminas,as well as conversion of one traditional alumina to another, is afunction of both time and temperature. Heating to a high temperature fora short time could result in a mixture of transitional aluminas havingthe same composition as is produced by heating the same starting mixtureor ingredient to a given lesser temperature for a longer time. Generallyspeaking, alpha alumina trihydrate is converted to the alphamonohydrate, a transitional alumina of this invention, at about 140 C.in air or superheated steam, and at about C. in vacuum. Beta aluminatrihydrate appears to be readily converted to the alpha monohydrate atabout 160 C. Heating of the alpha trihydrate to about C. for one hourresults in some conversion to the chi transitional form which is anothertransitional alumina of this invention. The chi form, in turn, goes overto some extent to the kappa transitional alumina when heated to about500 C. for one hour. Heating of the alpha monohydrate for one hour at250 C. gives some gamma, which on heating at 850 C. for the same lengthof time, produces some theta transitional alumina with possibleintermediate conversion to delta. Heating of the beta trihydrate to 140C., in addition to producing some alpha monohydrate, also produces someof the eta activated form. This, in turn, goes over to the theta onheating at 450 C. The kappa and theta forms are converted to alphaalumina on heating to 1150 C. for one hour.

Amorphous alumina, the third transitional alumina of this invention canbe obtained from either alpha or beta trihydrate. Amorphous alumina isfrequently encountered in the decomposition of alumina compounds, in theprecipitation of alumina, and in the oxidation of alumina.

In general then, the transitional aluminas used in this invention areprepared by heating a starting alumina selected from the classconsisting of alpha alumina trihydrate and beta alumina trihydrate to atemperature of at least 100150 C. for a period of time sufficient topermit substantial conversion to chi, alpha monohydrate, and amorphousforms of transitional alumina, but insufficient to convert a substantialfraction of these transitional aluminas to other phases. In general,prolonged heating above about 800 C. should be avoided. Our carriers maycontain small amounts of either the starting material, transitionalaluminas other than those of this invention, alpha alumina, or acombination of the aforesaid.

The three requisite forms of alumina may be formed independently andphysically mixed, or they may be prepared simultaneously. However, dueto economic considerations, the latter technique is preferred.

One method of large-scale preparation of the alumina carriers of thisinvention is as a by-product of the Fickes- Sherwin modification of theBayer process in the manufacture of metallic aluminum. During theprocess, aluminum trihydrate is precipitated from alkali aluminatesolutions. This material, a scale-like deposit, is then crushed orground and calcined at a temperature between 300 and about 800 C. Thefinished material comprising a mixture of the chi, alpha monohydrate,and amorphous forms of transitional alumina, is used primarily as acommercial adsorbent. It does not readily pack, can be used inhigh-pressure applications, and, after use, can be readily regenerated.

Certain aluminas meeting the requisites of this invention arecommercially available. Included among these are those sold by AluminumCompany of America as Desiccant Grade Active Aluminas; Grade F-1 and F3.

11 Minimum.

Both F-l and F-3 aluminas are composed of approximately 40 percent alphamonohydrate, 40 percent chi, and percent amorphous forms of alumina.

We have also found that under certain conditions, the inclusion of asmall amount of another metal or metals may further enhance theproperties of our catalysts. The additional metal or metals act as apromoter-; that is, though in themselves they may have little activity,they impart better characteristics to the finished catalysts. Generally,promoters serve to improve the activity, stability or selectivity forthe reaction in question, and oftentimes it is difficult to make adistinction as to their specific function. We have found that theinclusion of up to 10 percent, based on the total Weight of thecatalyst-carrier system, of a promoter metal or metals may, to a degree,improve efiiciency and life of the catalysts of this invention. Thepromoter in the finished catalyst is usually in an oxide form, but insome cases, e.g. silver, it may exist as the free metal. Metals that maybe used as promoters include sodium, lead, potassium, magnesium,calcium, strontium, barium, titanium, zirconium, iron, cobalt, nickel,copper, zinc, cadmium, germanium, tin, silver, cerium, cesium, and thelike. These metals may be introduced during preparation of the catalystsas salts such as the nitrate, acetate, carbonate, and the like, or inthe form of oxides or hydroxides, or even as the finely divided metalitself. A less desirable method is to impregnate a finished manganeseoxide-alumina catalyst with a promoter metalin one or more of the aboveforms.

The catalysts of this invention may be prepared in a variety of ways.They may be prepared by contacting the activated transitional aluminawith a solution, not necessarily aqueous, of an organic or inorganiccompound of manganese, allowing suflicient time for impregnation, andthen subjecting the mass to appropriate conversion treatment. Theconversion consists of thermal treatment to remove free water from thesystem, to convert the manganese to the oxide form, and to convert thepromoter metal to its active form. A great variety of specificconversion techniques are well known to those skilled in the art. If itis desired to impregnate the alumina with both a catalytic agent and apromoter, the alumina can be contacted successively With a solution ofeach metal in either order, or with one solution containing both metals.The catalysts can be prepared from organic compounds of manganese suchas the cyclopentadienyl derivatives, the carbonyl derivatives, etc.Examples are cyclopentadienyl manganese tricarbonyl, dimanganesedecacarbonyl, cyclopentadienyl manganese benzene, etc. Preferably, thecatalysts are prepared from manganese nitrates, carbonates, acetates,sulfates, hydroxides, "lactates, formates, acetates, oxalates,propionates, benzoates and the like. The same general types of salts areuseful for impregnating the substrate with a. promoter metal or metalswhen a promoter is desired. We have found that superior catalysts can beprepared by using nitrates, oxalates or acetates of the metals.Particularly excellent results are obtained when an acetate or a nitrateof the metal is used as the starting material. Other methods ofpreparing mixtures of transitional aluminas and manganese oxides canalso be used. For example, the manganese oxide may be incorporated intothe transistional alumina during the conversion of the starting aluminato the transitional form.

The following examples are illustrative of some of our preferredcatalysts.

Example I F-h grade alumina pellets are washed in lukewarm water toremove fines and extraneous matter, drained, then mixed with crystallinemanganese acetate tetrahydrate. F-l transitional alumina is prepared bycalcination of alpha alumina trihydrate and comprises a mixture ofaprroximately 40 percent chi, 40 percent alpha monohydrate, and 20percent amorphous forms of transitional aluminas described earlier inthis specification. The mixture is stirred and heated, the manganeseacetate tetrahydrate melting in its own Water by hydration. Heat isapplied up to a point wherein all the free Water has been evaporated. Atthis point the alumina pellets are coated With manganese acetate andhave a slightly moist texture. The mixture is then spread on a surfacewhich is heated to above the decomposition temperature of manganeseacetate. A draft of air or inert gas is then passed over the material.During the heating, the manganese acetate decomposes to an oxide ormixture of oxides. Our studies have shown that both the Mn O and Mn Ooxides are present. The finished material is F-l alumina impregnatedwith oxides of manganese. In this example the finished catalystcontained 0.5 percent manganese. This concentration is determined by therelative amounts of alumina and manganese acetate used in thepreparation.

Example II The procedure of Example I is followed but an amount ofmanganese acetate tetrahydrate is used such that the finished catalystis composed of 15 percent manganese in an oxide form.

Example Ill The procedure of Example I is followed using as the sourceof manganese a 5050 mixture of manganese acetate tetrahydrate andmanganese nitrate, but the amount of manganese saltsused is such thatthe finished catalyst is composed of 25 percent manganese in an oxideform.

Example IV A transitional alumina composed of 10 percent alpha aluminamonohydrate, 5 percent amorphous alumina and percent of chi alumina ismixed with a solution of manganese acetate and lead acetate. Thesolution is heated so as to evaporate all the free water and theprocedure of Example I followed. The finished catalyst is transitionalalumina impregnated with oxides of manganese and lead, comprising byWeight 10 percent manganese and 5 percent lead.

'3 Example V The procedure of Example IV is repeated using a solution ofmanganese acetate and copper acetate. The final catalyst materialcomprises transitional alumina impregnated with oxides of manganese andoxides of copper. The catalyst contains about 15 percent manganese and 2percent copper. The transitional alumina used in this catalyst comprisesa mixture of 45 percent amorphous alumina, 30 percent chi alumina and 25percent alpha alumina monohydrate.

Example Vl F-3 alumina is mixed with a solution of manganese acetate andchromium acetate and the solution is heated to evaporate all the freewater and the procedure of Example I is followed. This granulartransitional alumina is made by controlled calcination of alpha aluminatrihydrate and comprises a mixtureof approximately 40 percent chi, 40percent alpha monohydrate, and 20 percent amorphous forms oftransitional alumina. The finished catalyst is F-3 alumina impregnatedwith oxides of manganese and chromium, comprising 10 percent manganeseand 5 percent chromium.

Example Vll Transitional alumina is mixed with a solution of manganeseacetate and barium acetate and the solution is heated to dryness and theprocedure of Example I followed. The finished catalyst is transitionalalumina impregnated with oxides of manganese and barium comprisingpercent barium and percent manganese. The transitional alumina iscomposed of approximately 85 percent alpha alumina monohydrate, 10percent chi and 5 percent amorphous alumina.

Example VIII A colloidal aqueous suspension of titanium acetate is mixedwith a solution of manganese acetate. F-1 transitional alumina isintroduced into the resulting mixture, and the procedure of Example I isfollowed. The finished catalyst is F1 alumina impregnated with oxides ofmanganese and titanium, comprising by weight 7 percent manganese and 2percent titanium.

Example IX A catalyst is prepared using amounts of manganese acetate andcerium acetate such that the finished catalyst comprises transitionalalumina impregnated with oxides of manganese and cerium comprising byweight 5 percent manganese and 3 percent cerium. This transitionalalumina comprises a mixture of 50 percent alpha alumina monohydrate,percent chi, 18 percent amorphous alumina, and minor amounts of otherforms of transitional and alpha alumina.

Several catalysts of this invention and a variety of other catalystswere tested using the exhaust gas of a CFR L-Head, 7:1 compressionratio, single cylinder engine. As a preliminary test, the exhaust gaswas split into two streams and two different catalysts were testedsimultaneously. Each stream was passed over a catalyst bed consisting of42 cubic inches of a catalyst material. A secondary air supply, toprovide oxygen for the oxidation, was introduced into the exhaust gasstream just prior to the catalyst bed. This air supply was constantthroughout the testing period. In a subsequent test the total exhaustgas from the engine, together with some secondary air, was passed over acatalyst bed consisting of 86 cubic inches of the catalyst material.During both tests the engines were continually cycled, seconds under o 0idling conditions, and 150 seconds at wide-open throttle. The operatingconditions for the two tests are as follows:

TABLE I Engine operating conditions In the first test, namely,determination of oxidation efficiencies of a variety of catalysts bypassing exhaust gas over the 42 cubic inch bed, the engine was operatedon a non-leaded gasoline of the following composition:

Fuel composition ASTM distillation: F. Initial boiling point 97 10percent evaporated 148 50 percent evaporated 266 percent evaporated 327Final boiling point .422

Hydrocarbon type, vol. percent:

Aromatics 4O Olefins 4 Saturates 56 Sulfur, wt. percent 0.016

The hydrocarbon and carbon monoxide concentrations of the exhaust streamwere measured before and after passage through the catalyst bed. Allmeasurement were obtained under equilibrium conditions at wide-openthrottle.

The compositions of some of the catalysts investigated in this test areshown in Table II. Various metals are listed as active agents. It willbe understod that by this designation is meant the indicated metal(s) invarious oxide forms.

TABLE II Catalyst compositions CATALYSTS NOT OF THIS INVENTION CarrierActive Catalyst agent(s) Composition Surface area,

mfl/g.

A Mn, Pb.-. Silicon carbide nil B Mn, Pb 50% alpha alumina mono- 350hydrate: 50% gamma alumina (6% silica).

C V do 350 D Mn, Sn do 350 CATALYSTS OF THIS INVENTION E Mn F-l alumina:40% chi alu- 210 mina; 40% alpha alumina monohydrate; 20% amorphousalumina (0.09%

silica). Mn, Ti do Mn, Sn do Mn, Pb.-. F-3 alumina: 40% chi alu- 200mina; 40% alpha alumina monohydrate; 20% amorphous alumina (0.09%

silica).

The results of these tests, as percent of hydrocarbon and carbonmonoxide oxidized, are summarized in Table III.

TABLE III Oxidation efiiciencies of various catalysts ENGINE OPERATED ONNON-LEADED FUEL Catalysts not of this invention Catalysts of thisinvention Catalyst A B C D E F G H Active agent Mn, Pb Mn, Pb V Mn, S11Mn Mn, Ti Mn, Sn Mn, Pb

Hydrocarbon reduction, percent Test hours Carbon monoxide reduction,percent 11 Not determined.

The resutls of the preceding tests show that catalysts 25 carrier forthe manganese catalyst was F-1 alumina, a

E through H, catalysts of this invention, are superior to otherwisesimilar catalysts but utilizing different carrier materials. T he aboveresults permit a direct comparison of otherwise similar catalysts butdiffering in a critcial property. For example, catalysts A, B and H areall manganese-lead catalysts. However, these catalysts use differentcarrier materials and gave vastly different results. Catalyst A, usingsilicon carbide as a carrier, was an ineffective catalyst.

The eifectiveness of catalyst B in oxiding carbon monoxide was very low,and thus this catalyst is unacceptable for the purpose contemplated. Thecarrier of this catalyst is a transitional alumina, but because of itshigh silica content is not useable in this invention. Also, the carrierdoes not contain the required chi and amorphous forms of alumina. Incontrast, manganese-lead catalyst H, using a carrier material of thisinvention, showed superior properties. Note particularly the highefliciency with respect to oxidation of carbon monoxide as compared tocatalyst B.

Similar comparisons are available between manganesetin catalysts D andG. Catalyst G, using a carrier material of this invention, was clearlysuperior to catalyst D which used a transitional alumina carrier nothaving the requisite chi and amorphous forms of tranistional alumina.Also, this carrier had a silica content greater than that allowable forcarriers of this invention.

The above tests clearly show that manganese catalysts using the carriermaterials of this invention are superior to otherwise similar catalysts,but which use alumina carriers not having the specified properties.

Catalyst C, composed of vanadium pentoxide on a transitional alumina,though fairly active with respect to hydrocarbon oxidation, showed anextremely low efficiency (22 percent) toward promoting the oxidation ofcarbon monoxide. The carrier material of this catalyst was composed ofgamma and alpha monohydrate and, therefore, is not useable as a carrierfor the catalysts of this invention.

Further investigations were conducted on a variety of catalysts using afuel leaded to 3.0 grams of lead per gallon as tetraethyllead. Theexhaust gas was passed over a catalyst bed consisting of 86 cubicinches. This test was conducted under the conditions described in TableI above. The oxidation efliciencies of a vanadium pentoxide-aluminacatalyst and a manganese oxide catalyst of this invention are comparedin Table IV. The composition of the carrier for the vanadia catalyst wasessentially the same as for catalyst B described in Table II (gamma andalpha monohydrate aluminas), and the carrier of this invention.

TABLE IV Oxidation eficiencies ENGINE OPERATED ON FUEL CONTAINING 3.0ML.

TETRAETHYLLEAD Hydrocarbon reduction, C0 reduction,

percent percent Test hours Vanadium Manganese Vanadium Manganesepentoxide on oxide on F-l pentoxide on oxide on F-l transitionaltransitional transitional transitional alumina B alumina alumina ealumina Transitional alumina not of this invention. b Not determined.

It is apparent that both catalysts have excellent properies with respectto oxidizing the unburned hydrocarbon constituents of exhaust gases. Theefficiencies of both are as high as about 85 percent during the initialpart of the test. Even after 125 hours of testing, both catalysts showedan efficiency of over 60 percent. However, the catalyst of thisinvention is remarkably superior in the oxidation of carbon monoxide.Whereas the efficiency of the vanadium pentoxide catalyst in oxidizingcarbon monoxide was only about 20 percent or less throughout the test,the catalyst of this invention showed effioiency of over percent duringthe initial testing period. Even after hours of use, it still retainedan efliciency of 52 percent. This is a very important feature of thecatalysts of this invention since the elimination of carbon monoxide isequally if not more important than the elimination of the unburnedhydrocarbons.

Tetraethyllead, a constituent of the vast majority of commericalgasolines, is known' as a poison to many catalysts. To further determinethe resistance to poisoning of the catalysts of this invention, enginetests were conducted using a fuel containing an exaggerated amount,namely 12 grams per gallon of lead as tetraethyllead, rather than theamount ordinarily found in gasolines (24 grams per gallon).

The compositions of some of the catalysts evaluated under theseconditions are shown in Table V, and the oxidation efficiencies in TableVI.

1 1 TABLE v Catalyst compositions CA 'DALYSTS N'O'l OF THIS INVENTIONCarrier Active agent (s) Surface area,

Composition 50% alpha alumina monohy- 350 drate; 50% gamma alumina (6%silica).

Alpha alumina (0.02% silica).. 0.5

CATALYSTS OF THIS INVENTION F-l alumina: 40% chi alu- 210 mina; 40%alpha alumina monohydrate; amorphous alumina (0.09% silica).

F-3 alumina: 40% chi alumina; 40% alpha alumina monohydrate; 20%amorphous alumina (0.09% silica).

F-l alumina: 40% chi alumine; 40% alpha alumina monohydrate; 20%amorphous alumina (0.09% sillca).

M11, Ti- 210 TABLE VI Oxidation e ficiencies of various catalysts Notdetermined.

Under the conditions of this test, the catalysts of this invention showan even greater advantage over other catalysts that were tested. Thevanadia pentoxide-transitional alumina catalyst K had very lowefficiency with respect to oxidation of both hydrocarbon and carbonmonoxide. Similarly, catalyst L, manganese oxide on alpha alumina, wasvery ineffective. Both these catalysts are unacceptable for the purposeof this invention. In contrast, catalysts M, N and 0, preferredcatalysts of this invention, promoted the oxidation of both hydrocarbonsand carbon monoxide to a high degree. Even after being in use for 75hours, these catalysts were much more active than were catalysts K and Lat the beginning of test. High efliciency over long periods of time isone of the features of the catalysts of this invention.

An important feature of the catalysts of this invention is theirexcellent thermal stability properties. The catalyst bed temperatureunder normal engine operation may vary from 400 to 1700 F. Under extremeconditions of severe acceleration and deceleration, bed temperatures ashigh as 2000 F. have been observed. Using catalysts of this invention,catalyst beds have been operated at temperflillIQi as high as 2200 F.with no apparent damage to the catalyst material. The property of heatstability is very important because it obviates the necessity ofinstalling a mechanical system to have the exhaust gas by-pass thecatalyst bed in case of extremely high temperatures. Such a by-passsystem would be required if the catalyst were susceptible to damage athigh temperatures. Good thermal stability is also desirable in that itallows the reaction to be carried out at higher temperatures whereinhigher efiiciencies may be attained. Furthermore, this property becomesimportant when con sidering the design of a commercial vehicle exhaustsystem incorporating an oxidation catalyst. The additional heat from theoxidation process would naturally tend to overheat the passengercompartment. This problem could be solved by insulating the catalyst bedand exhaust system. Of course this would be possible only if thecatalyst could tolerate the higher temperatures due to the insulation.

Still another important feature of the catalysts of this invention istheir ability to catalyze reactions at extremely low temperatures. Sincecatalyst activity generally increases with temperature, in manyapplications it can be optimized by the simple expediency of increasingreaction temperatures. However, in exhaust gas conversion, temperaturescannot readily be controlled and a rather anomalous requisite of highactivity at both low and high temperatures is imposed. The catalysts ofthis invention are active at a temperature as low as 350 F.; i.e.,temperatures below that of the exhaust gas stream. Of course, as theoxidation starts, the heat of reaction serves to raise bed temperaturesto a much higher level.

A further important requisite of a catalyst for this application is thatthe oxidation go to completion rather than to yield incompletelyoxidized products such as olefins, aldehydcs, ketones, etc. Suchproducts tend to react with other atmospheric constituents andsubstantially contribute to photochemical smog. Moreover, many of theseproducts have very disagreeable odors. Our tests have shown that usingthe catalysts of this invention, the oxidation of hydrocarbons isessentially a complete reaction, resulting in substantially a completeconversion to carbon dioxide and water. The final product discharged tothe atmosphere is essentially free of any noxious odors.

Another feature of the catalysts of this invention is their ability tocatalyze the oxidation of hydrocarbons and carbon monoxide without theconcomitant oxidation of nitrogen. This is an important consideration.Oxides of nitrogen, and their subsequent reaction products readilycontribute to the formation of photochemical smog and are eye andrespiratory irritants.

Catalysts of this invention have been tested under actual operatingconditions in modern automobiles With excellent results; namely,substantial and essentially complete oxidation of hydrocarbons andcarbon monoxide, a discharge exhaust gas substantially free of noxiousodors, activity at both high and low temperatures and under a Widevariety of operating conditions, resistance to poisons in the exhauststream, particularly lead salts, and resistance to attrition due tophysical shock. With regard to poisoning by sulfur in the gasoline, bestresults are achieved at higher operating temperatures, particularly whenthe sulfur content of the gasoline approaches a high level. In general,when using gasolines with moderate to high sulfur concentrations, use ofhigher operating temperatures when possible is recommended. When loweroperating temperatures are used, the sulfur content of the gasolineshould be kept below about 0.06 weight percent.

The fuels used during these tests contain a variety of modern fueladditives and the catalysts were remarkably resistant to poisoning fromthese varied sources. The vehicle tests, conducted under typical unbanand country driving conditions, provided an opportunity to investigatethe effects of physical and thermal shock on the catalyst 13 material.These tests revealed that in spite of the many shocks and continualagitation, the resistance to attrition of the catalysts of thisinvention is such that special mechanical contrivances are not requiredto safeguard the catalyst material. The catalyst is simply put into asuitable container with openings to receive and discharge the exhaustgases. To firmly retain the catalyst material, the receiving anddischarge openings are covered with wire screening. The container mayhave internal baffling to allow greatest contact between catalyst andexhaust gas, and/ or to use the hot reaction gases to heat the incomingexhaust gases. The container may actually replace the vehicle muffier,or it may be incorporated into the conventional exhaust system ofcurrent vehicles. The catalyst bed may also be located in the exhaustmanifold or in the tailpipe of the exhaust system.

t1 aid the oxidation, secondary air may or may not be introduced intothe system. To obtain maximum efficiency, we have found it preferable tointroduce secondary air into the system. This is accomplished by the useof a variable speed blower, so that the amount of secondary air varieswith operating conditions. secondary air supply may also be introducedas a natural flow through the use of an appropriate air scoop or thelike.

Our catalysts can be used to convert the exhaust gas of any gasoline.The gasolines can be of the aliphatic, aromatic and olefinc typeincluding both straight run and catalytically produced gasolines and anyand all mixtures thereof. The gasol-ines can contain the usual additivesincluding organolead and other antiknock agents, such as tetraethyllead,tetraphenyllead, tetramethyllead, mixtures of alkylleads, such astetraethyllead-tetramethyllead mixtures, ferrocene, cyclopentadienylmanganese tricarbonyl, cyclopentadienyl nickel nitrosyl, scavengeres,antioxidants, dyes, deposit modifiers, including trimethyl phosphate,dimethylphenyl phosphate, and the like. A particular advantage to use ofthe present catalysts with gasolines containing cyclopentadienylmanganese tricarbonyl antiknock agents is that such antiknock agentsactually rejuvenate a catalyst whose activitiy has descreased due to thepoisoning and coating effects of gasoline constituents. This isespecially true with regard to the poisoning effects of oxides of sulfurpresent in the exhaust gas.

In addition to use in spark ignition internal combustion engines, thepresent catalyst may also be used to reudce or eliminate unburnedhydrocarbons and carbon monoxide from the exhaust products of combustionprocesses in general. This includes the compression igr1ition engine,oil and coal furnaces, residual fuel burners, etc.

We claim:

'1. A catalyst composition especially adapted to substantially oxidizethe unburned hydrocarbons and carbon monoxide constituents of theexhaust gas of internal com- The bustion engines, said compositionconsisting essentially of a major portion of a transitional alumina, andmangan se oxide in amount corresponding to from about 0.5 to about 25percent by Weight of manganese as said oxide, said transitional aluminacomprising from 10 to about 85 percent chi, from 10 to 85 percent alphaalumina monohydrate and from 5 to percent amorphous forms of alumina,said transitional alumina further characterized by having a silicacontent of from 0.02 to about 5 percent silica and having a surface areaof at least square meters per gram, said composition additionallycontaining from about 0.5 to 10 percent by weight of titanium as apromoter metal.

2. A catalyst composition especially adapted to sub stantially oxidizethe unburned hydrocarbons and carbon monoxide constituents of theexhaust gas of internal combustion engines, said composition consistingessentially of a major portion of a transitional alumina, and manganeseoxide in amount corresponding to from about 0.5 to about 25 percent byweight of manganese as said oxide, said transitional alumina comprisingfrom 10 to about percent chi, from 10 to 85 percent alpha aluminamonohydrate and from 5 to 45 percent amorphous forms of alumina, saidtransitional alumina further characterized by having a silica content offrom 0.02 to about 5 percent "silica and having a surface area of atleast 75 square meters per gram, said composition additionallycontaining from about 0.5 to 10 percent by Weight of tin as a promotermetal. i

3. A catalyst composition especially adapted to substantially oxidizethe unburned hydrocarbons and carbon monoxide constituents of theexhaust gas of internal combustion engines, said composition consistingessentially of a major portion of a transitional alumina, and manganeseoxide in amount corresponding to from about 0.5 to about 25 percent byweight of manganese as said oxide, said transitional alumina comprisingfrom 10 to about 85 percent chi, from 10 to 85 percent alpha. aluminamonohydrate and from 5 t 45 percent amorphous forms of alumina, saidtransitional alumina further characterized by having a silica content offrom 0.02 to about 5 percent silica and having a surface area of atleast 75 square meters per gram, said composition additionallycontaining from about 0.5 to 10 percent by weight of lead as a promotermetal.

References Cited by the Examiner UNITED STATES PATENTS MAURICE A.BRINDISI, Primary Examiner.

1. A CATALYST COMPOSITION ESPECIALLY ADAPTED TO SUBSTANTIALLY OXIDIZETHE UNBURNED HYDROCARBONS AND CARBON MONOXIDE CONSTITUENTS OF THEEXHAUST GAS OF INTERNAL COMBUSTION ENGINES, SAID COMPOSITIONS CONSISTINGESSENTIALLY OF A MJOR PORTION OF A TRANSITIONAL ALUMINA, AND MANGANESEOXIDE IN AMOUNT CORRESPONDING TO FROM ABOUT 0.5 TO ABOUT 25 PERCENT BYWEIGHT OF MANGANESE AS SAID OXIDE, SAID TRANSITIONAL ALUMINA COMPRISINGFROM 10 TO ABOUT 85 PERCENT CHI, FROM 10 TO 85 PERCENT ALPHA ALUMNIAMONOHYDRATE AND FROM 5 TO 45 PERCENT AMORPHOUS FORMS OF ALUMINIA, SAIDTRANSITIONAL ALUMINA FURTHER CHARACTERIZED BY HAVING A SILICA CONTENT OFFROM 0.02 TO ABOUT 5 PERCENT SILICA AND HAVING A SURFACE AREA OF ATLEAST 75 SQUARE METERS PER GRAM, SAID COMPOSITION ADDITIONALLYCONTAINING FROM ABOUT 0.5 TO 10 PERCENT BY WEIGHT OF TITANIUM AS APROMOTER METAL.
 2. A CATALYST COMPOSITION ESPECIALLY ADAPTED TOSUBSTANTIALLY OXIDIZE THE UNBURNED HYDROCARBONS AND CARBON MONOXIDECONSTITUENTS OF THE EXHAUST GAS OF INTERNAL COMBUSTION ENGINES, SAIDCOMPOSITION CONSITING ESSENTIALLY OF A MAJOR PORTION OF A TRANSITIONALALUMINIA, AND MANAGANESE OXIDE IN AMOUNT CORRESPONDING TO FROM ABOUT 0.5TO ABOUT 25 PERCENT BY WEIGHT OF MANGANESE AS SAID OXIDE, SAIDTRANSITIONAL ALUMINA COMPRISING FROM 10 TO ABOUT 85 PERCENT CHI, FROM 10TO 85 PERCENT ALPHA ALUMINA MONOHYDRATE AND FROM 5 TO 45 PERCENTAMORPHOUS FORMS OF ALUMINA, SAID TRANSITIONAL ALUMINA FURTHERCHARACTERIZED BY HAVING A SLICIA CONTENT OF FROM 0.02 TO ABOUT 5 PERCENTSILICA AND HAVING A SURFACE AREA OF AT LEAST 75 SQUARE METERS PER GRAM,SAID COMPOSITION ADDITIONALLY CONTAINING FROM ABOUT 0.5 TO 10 PERCENT BYWEIGHT OF TIN AS A PROMOTER METAL.
 3. A CATALYST COMPOSITION ESPECIALLYADAPTED TO SUBSTANTIALLY OXIDIZE THE UNBURNED HYDROCARBONS AND CARBONMONOXIDE CONSTITUENTS OF THE EXHAUST GAS OF INTERNAL COMBUSTION ENGINES,SAID COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR PORTION OF ATRANSITIONAL ALUMINA, AND MANGANESE OXIDE IN AMOUNT CORRESPONDING TOFROM ABOUT 0.5 TO ABOUT 25 PERCENT BY WEIGHT OF MANGANESE AS SAID OXIDE,SAID TRANSITIONAL ALUMINA COMPRISING FROM 10 TO ABOUT 85 PERCENT CHI,FROM 10 TO 85 PERCENT ,ALPHA ALUMINA MONOHYDRATE AND FROM 5 TO 45PERCENT AMORPHOUS FORMS OF ALUMINA, SAID TRANSITIONAL ALUMINA FURTHERCHARACTERIZED BY HAVING A SILICA CONTENT OF FROM 0.02 TO ABOUT 5 PERCENTSILICA AND HAVING A SURFACE AREA OF AT LEAST 75 SQUARE METERS PER GRAM,SAID COMPOSITION ADDITIONALLY CONTAINING FROM ABOUT 0.5 TO 10 PERCENT BYWEIGHT OF LEAD AS A PROMOTER METAL.